1. Field of the Invention
The present invention relates to a technology in reading an adjustment document used for image adjustment by an image reading apparatus.
2. Description of the Related Art
Conventionally, an image forming apparatus has been used which processes document image data generated by reading a document by an image reading apparatus such as a scanner. For example, a scanner itself, or a copier, a facsimile machine, a complex machine of these or the like that processes image data of a document read by the scanner is used as such.
Here, document image data does not necessarily indicate an original image on a document due to a reading characteristic of an image reading apparatus. Thus, image adjustments such as an input γ adjustment for adjusting image density to reproduce specified image density and an MTF (Modulation Transfer Function)/matrix adjustment for adjusting densities of respective YMCK colors to reproduce specified colors are performed, for example, regularly such as after a specified number of documents are read or after the elapse of a specified time or when significant abnormality is found in image data to be output.
For example, according to a certain image adjustment technology, a white reference plate with a bar-code indicating a chromaticity value measured beforehand is bonded to a document table glass, and the light quantity of a light source and the level of an output signal when a document is read are adjusted so that an output signal obtained by reading the white reference plate has a chromaticity value substantially equal to that indicated by the bar-code.
According to another image adjustment technology, a reference chart including a plurality of gradation patches and bar-codes recorded with density reference values corresponding to the respective patches is read, correction ratios corresponding to the plurality of respective gradation patches are calculated from density values of the read gradation patches and the density reference values indicated by the bar-code, and a reading characteristic is corrected using a gradation table generated using the calculated correction ratios.
However, conventionally, there has been a possibility of a failure in reading the bar-codes due to the smear of a document table or the smear of the white reference plate or the reference chart in the case of reading the white reference plate or the reference chart. Thus, parameters used in an image adjustment processing such as the chromaticity values and the density reference values indicated by the bar-codes could not be obtained and the image adjustment processing could not be appropriately performed in some cases.